Modelling and Evaluation

Sample questions

Real questions from this chapter, as the app sets them. Tap Answer to see the answer and working.

Section A · multiple choice

1. 1.

   A true positive is when:

   1. the model makes no prediction
   2. the case is positive and the model predicts negative
   3. the case is negative and the model predicts positive
   4. the case is positive and the model predicts positive

   Answer

   (d) the case is positive and the model predicts positive

2. 2.

   A decision tree picks a sports activity: • Is it raining? Yes → Chess. No → next question. • Is the temperature above 29 °C? Yes → Swimming. No → next question. • Is the wind above 25 km/h? Yes → Football. No → Badminton. What does it pick on a day that is not raining, 29 °C, wind 31 km/h?

   1. Badminton
   2. Chess
   3. Swimming
   4. Football

   Answer

   (d) Football

   follow the questions from the top

3. 3.

   Labelled points: A(4, 1) blue, B(0, 7) blue, C(3, 6) blue, D(5, 5) blue, E(8, 1) blue. New point Q(2, 5). Which labelled point is nearest to Q? (Compare (x₁ − x₂)² + (y₁ − y₂)².)

   1. A
   2. D
   3. C
   4. B

   Answer

   (c) C

   A: 20, B: 8, C: 2, D: 9, E: 52

Section B · short answer

1. 4.

   Define TP, FP, TN and FN.

   Answer

   TP: positive predicted positive; FP: negative predicted positive; TN: negative predicted negative; FN: positive predicted negative.

2. 5.

   A model predicts whether an email is spam (positive = spam). Its results: 1. actual spam, predicted spam 2. actual not spam, predicted spam 3. actual spam, predicted spam 4. actual spam, predicted spam 5. actual not spam, predicted not spam 6. actual not spam, predicted not spam 7. actual spam, predicted not spam 8. actual spam, predicted not spam 9. actual spam, predicted spam 10. actual not spam, predicted not spam 11. actual not spam, predicted spam 12. actual spam, predicted spam Count the (a) true positives (b) false positives (c) true negatives (d) false negatives.

   Answer

   (a) 5; (b) 2; (c) 3; (d) 2

   right and positive = TP; wrong and predicted positive = FP; right and negative = TN; wrong and predicted negative = FN

Section C · long answer

1. 6.

   A model screens 100 eye scans: TP = 20, FN = 5, FP = 10, TN = 65. Find the accuracy and explain which error matters more here and why.

   Answer

   Accuracy (20 + 65) ÷ 100 = 85%; false negatives matter more, because people who need care are missed.

Fresh sheets for your child

In the app, every Modelling and Evaluation sheet is new: the app remembers the questions your child has already had and leaves them out. Print the sheet as a PDF, or use notebook mode and write the answers in a notebook.

Coming soon for Android and iPhone.

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